Boundary layer control apparatus for compressors



g- 19, 1953 'G. F. HAUS/MANN 2,848,155

BOUNDARY LAYER CONTROL APPARATUS FOR COMPRESSORS Original Filed Nov. 20,1950 W lua'enior George 1 H4z2smcfwa M92201: gy

United States Patent BOUNDARY LAYER CONTROL APPARATUS FOR COMPRESSORSGeorge F. Hausmann, Glastonbury,

United Aircraft Corporation, corporation of Delaware 1 Claim.

Conn., as'signor to East Hartford, Conn., a

This application is a division of application Serial No. 197,144, filedNovember 22, 1950, now Patent No. 2,73 8,921, by George F. Hausmann.

This invention relates to boundary layer control for compressors and thelike.

It is an object of this invention to provide a boundary layer controlmechanism for axial flow compressors whereby the boundary layer flowalong the walls of the compressor is continuously removed.

Another object of this invention is to provide a boundary layer controlof the type described comprising mechanism for removing the boundarylayer flow adjacent the inner and/ or outer wall of a compressor passageand exhausting the boundary layer to a low pressure region.

A still further object of this invention is to provide a boundary layercontrol of the type described wherein the boundary layer is removed fromthe inner compressor wall and is exhausted through spanwise passagesinternally of the compressor blades, and from such passages to a lowpressure region or to the region adjacent the outer ends of the blades.

These and other objects of this invention will become readily apparentfrom the following detailed description of the accompanying drawings inwhich:

Fig. l is a cross-sectional view of a gas turbine engine including anaxial flow compressor utilizing a preferred embodiment of thisinvention.

Figs. 2 and 3 are cross-sectional views illustrating modification of theFig. 1 construction.

Fig. 4 is a cross-sectional view illustrating another modification ofthis invention.

Referring to Fig. 1, a gas turbine engine is illustrated having an axialflow compressor section 12, a burner or combustion section 14, a turbine16 and an exhaust nozzle 18. The turbine 16 drives a shaft 20 which inturn supports and drives :a plurality of compressor blade rotors 22. Therotors 22 comprise a plurality of hub elements fixed together to form ahub which thus disposed carries a plurality of peripherally as well asaxially spaced impeller blades 24. The outer periphery 26 of the hubforms a downstream continuation of the inlet cone 28 thereby comprisingthe inner wall for the compressor passage 30. A casing 32 surrounds thecompressor thereby forming an outer wall for the passage 30 and maycarry a plurality of stator blades 34 which are successively interposedbetween the impeller blades carried by each of the rotors 22. Aplurality of fuel nozzles 36 may be provided for injecting fuel into theburner or combustion section 14.

In order to increase the efliciency of the compressor and the individualcompressor blades it is desirable to remove the boundary layer which maybuild up along the walls of the compressor passage 30. As illustrated inFig. 2, the rotors 22 carry flanged annular members 40 which form ascoop spaced from the inner wall 42 of the compressor passage 30. Thescoop 40 extends upstream and terminates in a lip which is locatedupstream of the compressor blade 24. The scoop 40 forms an annularchamber 43 with the inner wall; 42 of the compressor passage whichcommunicates via apertures 44 in the base of the rotor blades (see alsoFig. 3) with drilled passages 46 in each of the impellerblades 24. Thepassages 46 terminate in an opening '50 adjacent the trailing edge andthe outer extremity of the blade 24.

In a compressor passage as illustrated, a suction action is developedwithin the drilled passage 46 *by the pressure gradient between the rootand tip of the rotating blades. Since the pressure gradient isproportional to the diiference of the square of the tangential velocityat" the roots and tips of the'blades, alower pressure will exist at theouter extremity'of each of the rotating blades than at the root thereofthereby inducing flow through the chamber 43, the apertures 44, passages46 and out through the opening 50 adjacent the tip of the blades. Thusthe air is actually centrifuged outwardly from within the blade passages46 so that a pumping action occurs.

Since the area of an axial flow compressor passage is reduced at eachsuccessive downstream compressor stage, each successive scoop 40 extendsoutwardly into the stream a greater amount than the adjacent upstreamscoop. This result is produced by enlarging the diameter of eachsuccessive hub 22 in a downstream direction or by spacing eachsuccessive downstream scoop farther from the axis of rotation of therotors.

Fig. 4 illustrates another modification of the principles just describedwhich modification comprises the bleeding of boundary layer flow fromalong both the outer and inner walls 32 and 42, respectively, of thecompressor passage 30. In this version of the invention a scoop 60 isprovided adjacent the root end of the stator blades 34 and a secondscoop 62 is provided adjacent the radially extreme end of the statorblades 34. The scoop 60 inducts boundary layer air into an annularchamber 64 which communicates with drilled passages 66 in stator blades34, which passages in turn lead to the surrounding atmosphere via thepassage or restriction 68 in the outer casing 32. Similarly the scoop 62inducts boundary layer flow along the outer wall and emits this fluidinto a second annular chamber 70 also leading to the atmosphere by meansof the opening or restriction 72.

Since the boundary layer is removed from along the compressor walls at apoint downstream of the first compressor stage, the surrounding oratmospheric air will be of a lower pressure than that existing adjacentthe scoops 60 and 62. As a result, a continuous flow of boundary layerfluid is maintained from along the compressor walls to the outsiderelatively low pressure air.

Rather than exhausting boundary layer air via the openings 68 and 72 tothe atmosphere, it may be desirable as illustrated in Fig. 1 to conductthis fluid via passages to annular chambers 82 which surround the burneror combustion section 14. Thus, any desired portions adjacent the burnerarea or other critical areas can be cooled by the boundary layer flowwhich is removed from the compressor walls. This boundary layer flowwill then pass outwardly to the atmosphere if so desired. In order toimprove the flow of boundary layer air it may be desirable to dischargethe air via an opening 86 adjacent the exhaust nozzle 88. In this mannerthe ejec- -tor action of the turbine exhaust will improve the exit flowof boundary layer fluid and provide a pumping force.

As a result of this invention it is apparent that a simple yet eflicientboundary layer control apparatus has been provided whereby no externalpower is necessary to conduct boundary layer flow away from the walls ofan axial fiow compressor.

Although only certain embodiments of this invention have beenillustrated and described herein, it will be apparent that variouschanges and modifications may be made in the construction and thearrangement of the various parts without departing from the scope ofthis novel concept.

What it is desired to obtain by Letters Patent is:

In an axial flow compressor having a plurality of impeller blades, ahub, said blades extending radially from said hub and forming aplurality of rows, a casingsurrounding said impeller blades and formingwith said hub an annular passage having inner and outer walls convergingin a downstream direction, stator blades carried by said casing andextending across said annular passage in alternate rows cooperating withsaid impeller blades, scoops carried by the ends of at leastone .row ofstator blades adjacent said .hub and adapted to intercept the boundarylayer flow along the inner wall of said annular passage, said scoopsLinterceptingthe boundary layer at a point immediately upstream of theleading edge of said stator blades, passage means .in said statorbladesv .connecting said scoops with the outer radial ends of saidstator blades, a source of pressure lower than the pressure in saidcompressor, and scoop means carried by the outer radial ends of said onerow of stator blades and intercepting the boundary layer flow along saidouter walls immediately upstream of the leading edge of said statorblades, said scoop means having a fluid connection with said source.

References Cited in the .file of this patent UNITED STATES PATENTS2,332,'-322 Kraft Oct. '19, 1943 2,720,356 Erwin Oct. ll, 1955 FOREIGNPATENTS 619,722 Great Britain Mar. 14, 1949

